Generating an estimated altitude of a mobile device such as a mobile phone can be accomplished with accurate measurements of ambient temperature and ambient pressure measured by one or more reference sensors positioned at known locations, along with a local pressure measured by a local pressure sensor of the mobile device. One well-known approach for generating an estimated altitude of a mobile device uses a barometric formula depicted in Equation 1 below:
                                          h            user                    =                                    h              ref                        +                                                            RT                  ref                                gM                            ⁢                              ln                ⁡                                  (                                                            P                      ref                                                              P                      user                                                        )                                                                    ,                            (                  Equation          ⁢                                          ⁢          1                )            where g corresponds to the acceleration due to gravity, R is the universal gas constant, M is the molar mass of dry air, Puser is a measurement of pressure measured by a local pressure sensor of the mobile device, Pref is a measurement of pressure measured by a reference pressure sensor or an estimated reference pressure value for a reference altitude that is based on the measurement of the pressure measured by the reference pressure sensor, href is a known altitude of the reference pressure sensor or the reference altitude, and Tref is a measurement of temperature measured by a reference temperature sensor. In particular embodiments, href=0 for sea-level altitude.
Estimated altitudes that are generated using Equation 1 rarely match true altitude. Instead, the quality of an estimated altitude directly depends on systematic error caused by various conditions (e.g., drift of the local pressure sensor, artificial pressurization of buildings, weather conditions affecting a reference sensor and/or a mobile device's sensor, quantization from rounding/truncating data to save space in memory, or other reasons). The quality of the estimated altitude also depends on statistical error induced by noise of individual measurements of local pressure, ambient pressure and ambient temperature. Different systems and methods that address systematic error and statistical error are described in the disclosure that follows.